This study is designed to test the hypothesis that colonial bats are an important interepidemic reservoir host of eastern equine encephalomyelitis (EEE) virus in Southern New England and a mechanism for virus survival through the winter in a temperate climate. In the surveillance studies completed to date, EEE virus was not detected in blood and/or organ samples from approximately 300 feral bats of three colonial species collected during 1973 and 1974 in Massachusetts and Connecticut. Antibody to EEE virus was demonstrated in 1.9% of the bat sera tested so far. Laboratory studies indicate that Aedes aegypti and Culiseta mealnura mosquitoes will feed on nonhibernating bats and will transmit EEE virus from an avian host (baby chicks) to bats. Preliminary results suggest that nonhibernating Eptesicus fuscus may succumb to EEE infection, something that was not observed with hibernating E. fuscus. However, not all EEE infections in this species are fatal in nature as indicated by a 4.6% antibody prevalence rate (pilot study - 3.6%; 1973 - 5.4%) in nonhibernating adult E. fuscus collected in southern New England. Attempts are currently underway to expose Myotis lucifugus and Myotis keenii to infected mosquitoes and to monitor infection and immune responses under conditions simulating hibernation.